From the seventeenth century to the twentieth, most philosophers thought that when we act of our own free will our actions have causes. Hume argued brilliantly for the compatibility of freedom and causal necessity in his Enquiry Concerning Human Understanding, s.8. But the causes of our actions were not thought to be physical events. They were non-physical events called ‘volitions’ or ‘acts of will’.

What is an action? [asks John Stuart Mill] Not one thing, but a series of two things; the state of mind called a volition, followed by an effect. The volition or intention to produce the effect, is one thing; the effect produced in consequence of the intention, is another thing; the two together constitute the action. I form the purpose of instantly moving my arm; that is a state of my mind: my arm (not being tied or paralytic) moves in obedience to my purpose: that is a physical fact, consequent on a state of mind. The intention followed by the fact, or (if we prefer the expression) the fact when preceded and caused by the intention, is called the action of moving my arm. 1

These volitions too had non-physical causes. Mill and earlier thinkers like Locke and Hume conceived themselves, in the words of Gilbert Ryle, as

duplicating for the world of mind what physicists had done for the world of matter. They looked for mental counterparts to the forces in terms of which dynamic explanations were given of the movements of bodies. Which introspectible phenomena would do for purposive human conduct what pressure, impact, friction and attraction do for the accelerations and decelerations of physical objects? Desire and aversion, pleasure and pain seemed admirably qualified to play the required parts. 2

In the twentieth century philosophy took a physical turn. Instead of duplicating the world of physics to explain mind, philosophers made it include mind. It seemed intolerable that any physical movement should have a non-physical cause. Those who felt they had a mission to get rid of the supernatural saw human beings as its last refuge. A complete exorcism, it was felt, required us to admit that all our bodily movements, even those of our hands when we write and our tongue when we speak, are mere continuations of purely physical processes just as when one billiard ball hits another their movements after the impact are a continuation of their movements before. Our movements are caused by physical events in the brain, firings of neurones, and these have prior physical causes stretching back in time to before we 90were born or conceived. We can still say that we have feelings and beliefs and make acts of will; but only on condition that these too are physical. They are really states of the brain which arise from sensory stimulation and result in activity of the motor nerves. Our brains, like pocket calculators, are physical structures; and just as when we tap 2 + 2 = into our calculator, out comes the answer 4, so when light stimulates our eyes and sound our ears, out comes the Parthenon, The Art of Fugue or a new book on philosophy.